The present invention relates to a deinking composition for reclaiming waste paper, which is used in the preparation of regenerated pulp from printed waste paper such as newspaper, magazines, journals, wood-free paper, copying paper and computer printout paper and a method for using the deinking composition.
More specifically, the present invention relates to a deinking composition and a method of using the same, which are suitable for deinking printed waste paper through flotation, can provide high quality regenerated pulp having a high brightness and a low content of residual ink and can ensure a stable deinking operation.
There has long been known methods for reclaiming printed waste paper to give starting materials for paper-making. In particular, the reclaiming of printed waste paper has increasingly become important from the viewpoint of saving energy and natural resources as well as protection of environment and correspondingly there have been required for the development of techniques capable of providing high quality regenerated pulp having excellent properties such as a high brightness and a low content of residual ink.
In general, methods for deinking printed waste paper can roughly be divided into two groups, one of which is a washing method and the other of which is a flotation method. There have been known a variety of literatures and knowledges relating to these processing methods, deinking mechanisms and difference in quality between deinking compositions used in these processing methods. See, for instance, Pulp & Paper, 1986, Nov., p. 59; Pulp & Paper, 1989, Mar., p. 60; Pulp & Paper, 1990, Mar., p. 76; Pulp & Paper, 1989, Mar., p. 97; Japanese Journal of Paper Technology, 1980, Aug., p. 37; 1989 TAPPI Pulping Conference, p. 343; Japan TAPPI Journal, Vol. 36, p. 1029; Japan TAPPI Journal, Vol. 39, p. 747; and U.S. Patent Nos. 4,483,741 and 4,518,459.
When summarizing literatures and, knowledges and experieneces which have been obtained through practical operations, the washing method in general comprises the step of repeatedly diluting and dehydrating a pulp slurry, or removing separated and dispersed ink particles from the pulp slurry through a screen or with a washing equipment such as a centrifugal cleaner. In this method, the separation of ink is greatly dependent upon, principally, mechanical conditions for due to washing equipments such as a press, a screen and a cleaner. Moreover, the washing method suffers from various problems concerning consumption of natural resources and energy since the use of a large amount of water is required. In addition, the washing method is greatly dependent upon mechanical factors and, therefore, workability of each step is regarded as important. In particular, when a composition having an intensive foaming ability, in particular, a deinking composition is employed, troubles due to foams arise in each equipment or process and this leads to reduction of workability and a marked increase in consumption of electric power. Thus, a composition having a low foaming ability or foaming-inhibitory properties must be used in the washing mehods. Further the separated ink particles must be fine and well dispersed in a pulp slurry in order to improve the efficiency of removing the separated ink.
On the other hand, the flotation method mainly comprises removing separated ink particles from a pulp slurry by adhering the ink particles to foams generated in a flotator. Thus, the mechanism of the removal of ink for the flotation method is completely different from that for the washing method and in other words, inks are principally removed through chemical processes unlike the washing method. The deinking method in which the flotation process is adopted sometimes comprises a so-called washing or dewatering step, but the separated ink particles are mainly removed in the flotation process. The flotation method is advantageous in saving natural resources since the amount of water used in this method is smaller than that required for the washing method. To improve the effect of removing inks in the flotation method, the separated ink particles must be coagulated to form aggregates having a relatively large particle size. Moreover, an appropriate foaming ability is required for the flotation process since the separated ink particles must be removed through the adhesion thereof to foams in the flotation method. This foaming ability required for the flotation method is higher than that required for the washing method. On the other hand, if the foaming ability of a composition, in particular, that of a deinking composition is too high, various problems arise. For instance, it is difficult to scrape out foams during the flotation process and various troubles due to foaming arise in each step. This leads to the interruption of the operation and the yield of pulp is reduced. Accordingly, the deinking process cannot be carried out stably and it is sometimes difficult to obtain high quality regenerated pulp having a high brightness.
As has been discussed above in detail, the deinking mechanism for washing method is quite different from that for the flotation method and, therefore, they require the use of deinking compositions having different properties.
The flotation method has been adopted mainly in Japan and Europe because it can provide regenerated pulp having a brightness higher than that accomplished by the washing method and is excellent in saving in natural resources and energy as compared with the washing method. Moreover, the deinking method has recently been switched from the washing method to the flotation method likewise in the United States.
Until now, there have been filed a variety of patents relating to deinking compositions and methods for using the same. For instance, U.S. Pat. No. 4,518,459 discloses a deinking method using a deinking composition obtained by adding a predetermined amount of propylene oxide to the terminal hydroxyl groups of alcohols or ethylene oxide adducts of alkylphenols, or by modifying, with benzyl ether, the terminal hydroxyl groups of alcohols or ethylene oxide- or ethylene oxide/propylene oxide block-adducts of alkylphenols. However, the method of this U.S. Patent relates to a washing method, while the present invention relates to a flotation method. Thus, the functions and properties of the deinking composition according to the present invention are quite different from those of the compositions used in the U.S. Patent. More specifically, the U.S. patent relates to deinking compositions particularly suitable for washing methods which require low foaming abilities or low forming-inhibitory effects, while the deinking compositions of the present invention are designed such that they can ensure a stable operation during the flotation step and that they have appropriate foaming abilities.
DE-2143912 likewise discloses a deinking method which uses a deinking composition obtained by adding ethylene oxide and propylene oxide to an alcohol or an alkylphenol to a desired extent and the flotation step is carried out at a temperature of not less than the clouding point of the deinking composition, but the method does not provide a high quality regenerated pulp having a high brightness and a low content of residual ink.
Japanese Unexamined Patent Publication (hereinafter referred to as "J.P. KOKAI") Nos. Sho 51-84905, Sho 53-31804, Sho 55-51891, Sho 55-51892 and Sho 56-79795 disclose deinking compositions comprising alkylene oxide adducts of alcohols or alkylphenols. However, these deinking compositions have foaming abilities higher than those required for each step and cannot ensure stable operations during flotation since the foaming leads to interruption of the deinking operation and a decrease in the yield of the deinking method. In addition, the deinking compositions do not exhibit sufficient abilities of trapping ink particles during the flotation and hence fin not always provide high quality regenerated pulp having a high brightness and a low content of residual ink.
J.P. KOKAI No. Sho 61-41386 discloses the use of a composition comprising an alkylene oxide adduct of an alcohol and an ethylene oxide adduct of an alcohol, but the composition does not have an ability of trapping ink particles. The ethylene oxide adduct of alcohol used in this method rather has high ability of dispersing ink. Therefore, the flotation method using this deinking composition cannot provide high quality regenerated pulp and stable operability. J.P. KOKAI Nos. Sho 50-142804, Sho 61-186592, Sho 62-177291 and Sho 62-250291 disclose deinking compositions comprising alkylene oxide adducts of alcohols and higher fatty acids which can improve the ink-trapping properties of the alkylene oxide adducts of alcohols required for the flotation process. These compositions can improve the ink-trapping ability, but the use of these compositions makes it difficult to control foaming during flotation and to perform stable operation. J.P. KOKAI No. Sho 63-165591 discloses deinking compositions comprising alkylene oxide adducts of alcohols and alkylene oxide adducts of fatty acids for improving the ink-trapping ability of the alkylene oxide adducts of alcohols required for the flotation process. However, the use of these deinking compositions do not always provide stable operability during a deinking method in which a flotation process is included.
The deinking compositions disclosed in the foregoing German Patent and Japanese Unexamined Patent Publications do not always ensure stable operability and do not provide high quality regenerated pulp having a high brightness and a low content of residual ink, while the deinking composition provided by the present invention comprises a combination of two kinds of different specific deinking compositions which are designed such that they can ensure stable operation and can provide high quality regenerated pulp having a high brightness and a low content of residual ink. Moreover, the foregoing references do not disclose the influences of by-products simultaneously formed during the preparation of the deinking compositions on the deinking properties of the resulting deinking compositions.
Further Canadian Patent No. 729,071 discloses a deinking composition comprising an alkylphenol to which an alkylene oxide is added, but the deinking composition does not exhibit sufficient ink-trapping properties when it is used in the flotation method and cannot provide high quality regenerated pulp. In addition, it is not preferred from the viewpoint of protection of environment since alkylphenols are in general less biodegradable.
U.S. Pat. Nos. 3,021,372; 2,856,434; 2,903,486; 3,340,309; 3,444,242 and 3,625,909 disclose compounds which are prepared by adding alkylene oxides to alcohols or alkylphenols, but these compounds quite differ, in structures and applications, from those of the present invention. U.S. Pat. No. 4,162,186 also discloses a deinking composition, but the deinking composition comprises a combination of an oil-soluble alcohol ethoxylate with a water-soluble alcohol ethoxylate and completely differs from the deinking composition of the present invention.